Typical track-type vehicles, such as, for example, crawlers and excavators, have an undercarriage comprising wearable components that have a finite life in specific applications. Sprocket segments, rollers, idlers, track chain bushings, and track chain links eventually wear to a point where the part or assemblies have to be replaced. The undercarriage of a crawler, for example, accounts for approximately 35% to 40% of the total operating costs over the life of the crawler. Extending undercarriage life is therefore a great desire of end users, especially in high-wear applications, so as to reduce the cost per hour of running the undercarriage to a competitive level.
In the undercarriage of a typical track-type vehicle, the undercarriage has a number of tracks, one or more of which are located on each side of the vehicle. Each track has an endless track chain and a number of ground-engaging shoes fastened to the chain about the chain periphery. When assembled to the vehicle, the chain is trained in a closed loop about a drive sprocket, an idler, and a number of upper and lower rollers.
The chain has two endless rows of track chain links extending longitudinally of the chain and track chain joints laterally connecting the two rows. The chain is typically sealed and lubricated at the joints. With respect to each row, each joint connects two adjacent links for relative rotation between those links as the chain travels along its longitudinal dimension in its closed-loop path.
Each row includes a plurality of track chain links, master and non-master links. The master link of each row is used to open and close that row of the chain. Other than the master link, the links of each row are configured as non-master links. The shoes are typically mounted to the periphery of the links.
Over time, the chain will become worn. For example, in the case of a fixed-bushing chain, in which the bushing of each track chain joint is fixed to a link in each row, the external wear surface of the bushing may wear on one side due to repeated contact between the bushing and the drive sprocket. In such a case, to extend the life of the chain, the bushings are typically “turned” to present a fresh portion of the bushing external wear surface.
The turning operation involves taking the machine to a shop (e.g., at a dealer) that has a track press, taking the chain completely apart, and rebuilding the chain with the bushings turned 180 degrees so that a fresh portion then engages with the drive sprocket. This process is intensive, expensive, and typically can take between two to three days to accomplish. In addition, as the chain is completely taken apart, the bushing-to-link press-fits can be compromised; some material at the interface may be scored and chain integrity (e.g., the seals) may be jeopardized if the track press operator pushes the chain back together either too violently or not completely enough.
A crawler fitted with a fixed-bushing chain will typically incur some wear depending on its geographical area of operation. It is not uncommon for a larger crawler to obtain between approximately 1200 and 1400 hours of bushing life before the bushings are turned to take advantage of the unworn portion. In addition, repeated contact between the rail surface of each link and, for example, the rollers tends to scallop the rail surface.
A longer life, rotating-bushing chain may also experience wear. In such a chain, the bushings are rotatable, rather than fixed, relative to the links, so the bushings tend to wear less from contact with the drive sprocket and thus last longer than bushings in a fixed-bushing chain. However, repeated contact between the rail surface of each link and, for example, the rollers tends to scallop the rail surface, which eventually calls for replacement of the link.